The invention relates to smoke detectors of the type shown in U.S. Pat. No. 3,863,076 wherein the optical components of the detector, namely an exciter lamp and a photocell, are enclosed within a block pre-assembled around the cell and lamp and forming light passages on optical axes. The axes cross outside the block at an intersection where light from the lamp is scattered by smoke back to the cell. Herein photocell and lamp are meant to include all electrically photoresponsive tubes and solid state devices and all sources of light in the visible and adjacent spectrum including incandescent, discharge and solid state devices.
It is the object of the present invention to provide an improved optical block in which the photocell and lamp are most simply assembled in the optical block and mounted on a circuit board in the smoke detector.